Where the trustworthiness of digital data is important, it is known to use digital signatures to permit authentication of the digital data. When data is transferred from a sender to a recipient, the prior art provides a mechanism for the recipient to confirm that the received data is the same as the data as it was sent. A known technique is for the sender to compute a digest of the data before it is sent. The digest, and potentially other identifying data, makes up a digital signature. The digest is encrypted using a private key generated using a public key encryption standard (for example, the RSA encryption standard) and is attached to the sent data. A party seeking to authenticate the data is able to decrypt the digital signature (the data digest) using the public portion of the public-private encryption key pair. The recipient is able to compare the decrypted digest with the data received. If the decrypted digest conforms to the data actually received then the recipient of the data has an assurance that the data is the same as what was sent.
Due to the properties of the public-private pair of keys in the public encryption standard, the recipient can be assured that the digest of the data was generated by the party having access to the private key, only. In this way, the party using the data can ensure that the data has not been tampered with after the digest was encrypted by the party holding the private key.
In such a system the sender will make available the public key portion of the public-private key pair generated by the public key encryption system. This public key will permit any user having access to the public key to decrypt the digital signature which has been generated by the use of the associated private key.
Typically, in systems such as that described above, a given public-private key pair will be valid for a certain period of time, following which a new public-private key pair is generated. To ensure that the public key remains useful during the stipulated time period, it is known to save, in a secure manner, the private key, to ensure that if the system generating data is restarted for any reason, the private key will be available for use digitally after the system is restarted.
As will be apparent, the security of this system is compromised where the private key is not securely stored. In the prior art different approaches are used, including the use of smart cards for the storage of private keys, to keep the private keys secure.
Such approaches, however, either make the private keys potentially vulnerable to breaches of security or incorporate potentially expensive and complex security mechanisms to maintain the private key in a secure manner.
It is therefore desirable to have a digital signature system in which the private key may be maintained in a secure manner without requiring complex security mechanisms.